An Argument that sometimes fools human reasoning, but is not logically valid. It is crucial to remember that reasoning from definitions and facts to conclusions is fundamentally different from reasoning about definitions. Before you can scientifically establish whether or not Foo is a Bar, you have to establish the Meaning of the label Bar.
A given term is associated with one or more definitions and one or more concepts. A definition is correct when it accurately represents a chosen concept. Definitions can be more or less formal, the more formal the better. Concepts are not correct or incorrect, but merely useful.
NOTE: The list of logical fallacies should be restricted to those in actual Wiki usage.
[Please take discussion to Fallacious Arguments Discussion. Please. Pretty please?]
Formal Fallacies (incorrectly constructed logical syllogisms [well, they're not ''all' three part logical errors])
Antecedent Assumed Fallacy (A is true because of B, but B is true because of A) [similar to Circular Reasoning]
Argument By Analogy (A is like B; A has property P; therefore, B has property P) [is this similar to Composition Fallacy?]
Begging The Question (A hidden assumption supports the "proof" in process)
Circular Reasoning (A is because of B, which is because of C, which is because of A)
Post Hoc Ergo Propter Hoc (A follows B so B causes A)
Correlation Implies Causation (There is a demonstrated correlation between A and B, therefore A implies B) [same as Post Hoc Ergo Propter Hoc]
Non Sequitur (Conclusion does not follow from the premises)
Undistributed Middle (All A are C, All B are C, therefore all A are B)
Informal Fallacies (well-known) [These are fallacies you are likely to find in textbooks]
Ad Hominem (The person saying P is biased or otherwise flawed, so P is false)
Ad Verecundiam (P is true because person/entity X has said so)
Argument From Authority (quote someone famous) [equivalent to Ad Verecundiam]
Argumentum Ad Baculum (Argument from fear; "If you believe P, you'll suffer for it")
Argument By The Masses (aka Argumentum Ad Populum; A is true because "everybody knows it is true")
Equivocation Fallacy (using a term with multiple definitions as if the definitions were equivalent when they are not)
No True Scotsman (Assert that A conforms to B - redefine the identity of A until it does)
Red Herring (A is true because of totally irrelevant B)
Straw Man (a weak argument specifically put forth to be knocked down)
Argumentum Ad Infinitum (aka Argumentum Ad Nauseum; A argues longer/more eloquently than B, so A's proposition must be true)
Argumentum Ad Ignorantiam (if A can't imagine P to be true, it can't be true)
Disproof By Fallacy (aka Ad Logicam; Argument has been made at some point for A through error X, therefore A must be false)
Complex Question (A question contains an assertion assumed to be true, e.g. "Have you stopped beating your wife yet?")
False Dichotomy (aka Bifurcation Fallacy, This Or That Fallacy, False Dilemma; e.g. "You're either with us or you're with the terrorists."; See also Excluded Middle.)
Naturalistic Fallacy (Deriving "ought" from "is")
Informal Fallacies (colloquial) [Most of these are variants of other fallacies or otherwise suggested by contributors]
Argument From Intimidation (see also Immaturity Argument) [not the same as Argumentum Ad Baculum]
Absence Of Evidence Is Not Evidence Of Absence (We have never observed a proton decay, therefore it can never happen)
Anonymous Choir (there are people out there who agree with me)
Argument By Gibberish (utter things that turn on the lower third)
Argument From Incredulity (I can't believe any alternative is true)
Argument By Repeated Assertion (use "Saddam" and "Al Qaeda" together in the same sentence often enough and eventually they'll believe it, evidence or not)
Argument By Flame. ("C++ sucks. Bjarne Stroustrup is an idiot. People who use C++ are all lemmings. I'm not going to bother with any legitimate technical critique of C++ because I'm having too much fun flaming; plus I've a got an audience full of fellow-travelers who are lapping this stuff up and patting my back.")
Assumed Agreement Fallacy (So-and-so agrees with me on X, so he probably agrees with me on Y too).
Assumed Scalability Fallacy. (A works well as a small system; therefore it will work well as a large system. Or vice versa)
Avoiding The Question (The response to a question does not actually answer it).
Concepts Out Of Context (B pertains to A when B makes no sense in the context of this A)
Confusing Theory And Practice (practice of A > practice of B implies theory of A > theory of B or vice versa)
Desert Island Fallacy (New technology B should be abandoned in favor of old technology A, because B will fail if you're ever stranded on a desert island)
Disagree By Distorting (assume an example would be, You want the government to assume restricted responsibility X, therefore you must be a totalitarian socialist)
Dogmatic Fallacy (evidence against some X is excluded by the Universe Of Discourse)
Dueling Credentials (I know more about X than you do, so I win)
Everyone Has His Opinion (the opinion of a layperson is as good as that of an authority)
Evidence By Best Case Scenario (best case example may distract from problem domain)
Evil Or Stupid (If you don't agree with me, which one are you?)
Excerption Not Abstraction (dogs are animals with four legs, so what about amputated dogs?)
Failure To Elucidate (Using terms more obscure than the primary point at issue)
Gordian Reasoning (A is because of B, which is because of C, which is because of D... which is because of Y, which is because of Z, which is because of A) [an extended version of Circular Reasoning]
Grand Conspiracy (asserting that the world is being manipulated by a cabal of some sort)
Idont Suffer Fools Like You (Asserting that the opponent is unworthy of debate)
If It Aint Broke Dont Fix It (Arguing that older things are better than the newer ones)
If It Aint Scottish Its Crap (The merits of X can be determined by some superficial attribute of X)
If You Dont Like It You Dont Understand It (A lack of agreement implies a lack of expertise)
Invented Here (This can't be particularly good if you did it)
It Seems To Me (substituting opinion for evidence or reason)
Level Category Error (O is the set of all X. All X are drawn with 2 lines so O is drawn with 2 lines)
New Technology Has Failed (Because it doesn't live up to the hype)
New Technology Will Save Us All (A Disruptive Technology it is, trust us)
Not Invented Here (Arguing that the newest thing is better than the older ones.)
One Thing All Things (If you believe X about Y0, you must also about Y1...Yn | n is large)
Over Simplification (arguing on a level of detail that ignores important details)
Package Deal (You can't have A without B, and B is false, so A is false - even though you actually can have A without B)
Posthumous Ally (if X were alive, he'd agree with me)
Shifting The Burden Of Proof (P is false unless you prove it)
Slippery Slope (A might lead to A^n, which is bad, therefore A is bad)
Stolen Concept Fallacy (A presumes P which normally follows O, without proving O first)
Sweeping Generalization (Similar to Argument By The Masses)
Shifting The Universe Of Discourse (A doesn't count in the discussion of B [while it might]) [similar to No True Scotsman]
They Laughed At Einstein (expert opinion on a subject is not trustworthy)
Those Not Like Me Are All Alike (B != A and C != A, so B == C)
Well Designed Foo Can Be Better Than Bar (Some instance of A > some instance of B, so A > B)
Argumentum Ad Hitlerum (P is comparable to Hitler, and therefore evil)
Not all of the above are arguments, some are actions, approaches or strategies. Does that make this page false? According to Critical Success Factor, it does.
Critical Success Factor need not apply to a Wiki page for it to be useful. Let's not get carried away here.
See also Carl Sagans Baloney Detection Kit which has another list of Fallacious Arguments.
See original on c2.com 